The present invention relates generally to the field of olefin polymerization catalysis, supported catalyst compositions, methods for the polymerization and copolymerization of olefins, and polyolefins. More specifically, this invention relates to metal-containing sulfated activator-supports, methods for producing such activator-supports, and to catalyst compositions employing these activator-supports.
Polyolefin homopolymers, copolymers, terpolymers, etc., can be produced using various combinations of catalyst systems and polymerization processes. One method that can be used to produce such polyolefins employs a metallocene-based catalyst system. Generally, metallocene catalysts produce polyolefins with a narrow molecular weight distribution, and without a high molecular weight tail to the molecular weight distribution. While a polymer having a narrow molecular weight distribution can be advantageous in certain polymer processing operations and end-use applications, it can be a drawback in others. Stability in certain polymer processing operations, such as in blown film, blow molding, and pipe extrusion, often is reduced with a narrow molecular weight distribution polymer, as compared to broader molecular weight distribution polymers, resulting in reduced output or production rates. The high molecular weight tail, or fraction, of the molecular weight distribution can provide higher melt strength and/or higher zero shear viscosity to the polymer which can improve processability and certain end-use properties in blown film, blow molding, pipe extrusion, and other related applications.
Hence, it would be beneficial to produce a relatively narrow molecular weight distribution polymer—as compared to, for instance, a polymer produced using a chromium catalyst—using a metallocene-based catalyst system, where the polymer has a high molecular weight tail to improve processing and end-use properties in certain polyolefin end-use applications. Accordingly, it is to these ends that the present invention is directed.